Seasoned political observers eying this year’s race for Pierce County Prosecutor figured challenger Mary Robnett might get close to incumbent Mark Lindquist in this week’s primary election — but none predicted the lopsided result revealed in Tuesday’s returns.

In a surprising show of strength, Robnett outpointed Lindquist 55 percent to 45 percent in the first count of ballots. The result, an ominous sign for Lindquist, suggests the hard-fought campaign will get nastier between now and November.

Lindquist had no comment. Alex Hays, his longtime Republican consultant, offered a brief hint of things to come after examining the results.

“Mark focused on his own record of making the community safer rather than his opponent’s serious ethical and professional defects,” Hays said. “The campaign will take on the job of informing voters of his opponent’s record.”

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Reached Tuesday night, Robnett replied, “I’m delighted to run on my record. I think it’s clear that Pierce County’s ready for a change.

“I’m happy with the primary returns. I thought our campaign had a good showing. We’re going to party tonight, and we’re going back to work tomorrow.”

The campaign has been hard-fought and ranks as the most expensive county-level race in the state this year. The rivals have raised almost $400,000 for the race in a near-even split of contributions, with Robnett slightly ahead, according to the latest state campaign-finance reports.

Both sides have poured their money into online ads and mailings, spending roughly $280,000 collectively. Lindquist, 59, known for disciplined messaging, has emphasized his eight-year record, underlining programs such as an elder-abuse unit and a program aimed at prosecuting repeat offenders.

Robnett, 62, an assistant attorney general who worked in the prosecutor’s office from 1994 and 2012 and served as chief criminal deputy, has emphasized her own record, citing convictions obtained in high-profile cases involving some of the county’s worst crimes. She also has pointed to controversial elements of Lindquist’s tenure, including a costly fight to prevent disclosure of text messages and a damaging whistleblower report that revealed an office plagued by internal conflicts.

The race has fractured traditional partisan loyalties. Lindquist, a Democrat, bagged endorsements from scores of local elected officials, including Tacoma Mayor Victoria Woodards, members of the Tacoma City Council and Gov. Jay Inslee.

Robnett has countered with equally prominent endorsements from former Republican state Attorney General Rob McKenna and Democrat Pat McCarthy, former Pierce County executive and current state auditor. She’s also won the endorsements of the county’s largest law enforcement unions, and, unexpectedly, local Democratic organizations.